PALISADE enrolled 499 patients ages 4–17, 496 of whom received
treatment. After approximately one year of treatment, patients completed
an exit double-blind, placebo-controlled food challenge (DBPCFC). In the
primary analysis of 496 patients ages 4–17, 67.2% of AR101 patients
tolerated a single highest dose of at least 600 mg of peanut protein
(1043 mg cumulative) with no more than mild symptoms in the exit DBPCFC,
compared to 4.0% of placebo patients. The corresponding difference in
response rates was 63.2% (p<0.00001, 95% CI=53.0–73.3%), and, at 53%,
the lower bound of the 95% confidence interval greatly exceeded the
pre-specified success criterion, which was 15%. Additionally, 50.3% of
AR101 patients tolerated a single highest dose of 1000 mg of peanut
protein (2043 mg cumulative), compared to 2.4% of placebo patients
(p<0.00001). In order to minimize the risk of assessment bias, the
primary endpoint evaluations were conducted by independent, blinded
assessors, who were not involved in patients’ ongoing care in the trial
and who were blinded to treatment assignment and the sequence of the
DBPCFCs.

PALISADE enrolled a highly allergic patient population, and enrollment
was balanced for baseline disease characteristics between the two
treatment arms. Patients in the primary analysis group of ages 4–17
tolerated no more than 30 mg of peanut protein in the entry DBPCFC;
additionally, 72.2% had a past medical history of anaphylaxis, 53.0% had
a present or previous diagnosis of asthma, and 65.5% reported multiple
food allergies.

In the trial’s primary analysis group of ages 4-17, 496 patients from
both arms (372 AR101 and 124 placebo) were evaluable for safety. In both
arms, the incidence of serious adverse events (SAEs) was low. A total of
10 patients experienced SAEs, none of which were considered
life-threatening: nine of these patients were in the AR101 arm (2.4%)
and one was in the placebo arm (0.8%). Of the nine AR101 patients who
experienced a SAE, five patients experienced mild or moderate SAEs. The
other four AR101 patients experienced severe SAEs, which, for two of
these patients, were not related to treatment (a concussion and a viral
asthmatic exacerbation). Of the two patients who experienced severe SAEs
related to treatment, both of whom had elevated baseline peanut-specific
IgE levels greater than 100 kU/L, one experienced anaphylaxis, and the
other experienced wheezing on the first day of treatment. Both of these
patients discontinued from the study.

In ages 4–17, 20.4% of AR101 patients and 6.5% of placebo patients
discontinued the trial. In the AR101 arm, 12.4% of patients discontinued
due to investigator-reported adverse events, including 6.7% due to
gastrointestinal adverse events and 2.7% due to systemic allergic
hypersensitivity reactions. In the placebo arm, 2.4% of patients
discontinued due to investigator-reported adverse events.

Discontinuations in the AR101 Group1

AR101

(n=372)

%

n

Total discontinuations regardless of causality

20.4%

76

Discontinuations not related to adverse events

8.0%

30

Discontinuations related to adverse events

12.4%

46

• Gastrointestinal2

6.7%

25

• Systemic hypersensitivity reactions3

2.7%

10

• Respiratory system

1.1%

4

• Cutaneous

0.8%

3

• Other4

1.1%

4

1 Ages 4-172 Includes one case of
biopsy-confirmed eosinophilic esophagitis; no additional cases were
identified in the study3 Of these, seven were
investigator-identified anaphylaxis events (one severe)4
Includes one discontinuation for each: acute viral illness, eye
pruritus, headache, and an unknown factor

One patient (an 11-year-old boy), with a baseline peanut-specific IgE
level of 352 kU/L) was discontinued from the study after being found to
have biopsy-confirmed, moderate eosinophilic esophagitis during the
study. By the time the patient left the study, the symptoms had
resolved. No additional cases of eosinophilic esophagitis were
identified in the study.

Hypersensitivity reactions are an expected and common side effect of
oral immunotherapy. In PALISADE patients ages 4–17, 14.5% of AR101
patients experienced systemic hypersensitivity reactions, and for 98.2%
of those patients, the reactions were mild or moderate. In comparison,
3.2% of placebo patients experienced systemic hypersensitivity
reactions, and for all of those patients, the reactions were mild or
moderate.

Across all ages, there were no deaths or suspected, unexpected serious
adverse reactions (SUSARs) in the trial.

PALISADE included 55 adult patients ages 18–49 who were randomized into
the study, with 41 patients in the AR101 arm and 14 patients in the
placebo arm. In the AR101 arm, 21 patients discontinued treatment, eight
due to adverse events. In an exploratory analysis of this age group, 85%
of AR101 patients who completed the study tolerated at least 600 mg of
peanut protein in the exit DBPCFC, compared to 15% of placebo patients
who completed the study.

“It’s exciting to see this large-scale study confirm that a
characterized approach to oral immunotherapy, in an appropriately
supervised clinical setting, holds promise for becoming an approved
treatment,” said A. Wesley Burks, M.D., Executive Dean and Curnen
Distinguished Professor of Pediatrics, University of North Carolina
School of Medicine, and a principal investigator for PALISADE. “It’s
great to have patients go from managing to tolerate at most the amount
of peanut protein in a tenth of a peanut without reacting to
successfully eating the equivalent of between two to four peanuts with
nothing more than mild, transient symptoms, if any at all. Patients and
their families are highly motivated to pursue an effective treatment for
peanut allergy, and AR101 could give them a comfortable margin of safety
in case of accidental exposures.”

“We want to express our heartfelt gratitude to everyone who supported
the PALISADE trial, especially the investigators and their teams, our
employees, and, above all, the patients and their families,” said Daniel
C. Adelman, M.D., Chief Medical Officer of Aimmune. “PALISADE is not
only the largest peanut allergy trial ever conducted, it’s also the
first to use an independent blinded assessor, and the first to accept
peanut-allergic patients with a history of severe or life-threatening
reactions. Moreover, the PALISADE population was highly peanut-sensitive
and highly atopic, with almost three quarters of the patients having
experienced anaphylaxis prior to enrolling in the study. Given how
robust the PALISADE results are and that they met or exceeded the
pre-specified metrics, we’re very encouraged that the data from PALISADE
are helping to define the magnitude of the potential treatment effect in
very sensitive peanut-allergic patients.”

“We at Aimmune are enormously pleased with this result, but this success
really belongs to the entire food allergy community,” said Aimmune CEO
Stephen Dilly, M.B.B.S., Ph.D. “Aimmune was originally founded through
the commitment of food allergy parents, food allergy advocates, and food
allergy researchers. They all saw a future where a safe, reliable and
accessible medicine could protect people from terrifying allergic
reactions that occur because of innocent, inevitable mistakes. We remain
the custodians of their vision, and we are proud to be taking another
meaningful step toward delivering on it.”

Aimmune expects to submit a Biologics License Application (BLA) for
AR101 with the FDA by the end of 2018, followed by a Marketing
Authorisation Application (MAA) with the European Medicines Agency (EMA)
in the first half of 2019. In the United States, AR101 has FDA Fast
Track Designation, as well as FDA Breakthrough Therapy Designation for
peanut-allergic patients ages 4–17.

Conference Call and Webcast Information

Aimmune will host a conference call and live audio webcast today,
February 20, 2018, at 8:00 a.m. ET / 5:00 a.m. PT to discuss the topline
PALISADE results. The conference call and associated slide deck will be
accessible via the company’s website at www.aimmune.com
on the Events page under Investor Relations. Please connect to the
company’s website at least 15 minutes prior to the start of the
conference call to ensure adequate time for any software download that
may be required to listen to the webcast. Alternatively, participants
may dial 1-877-497-1438 (domestic) or 1-262-558-6296 (international) and
refer to conference ID 9079639. An archived copy of the webcast will be
available on the company’s website for at least 30 days after the
conference call.

About PALISADE

PALISADE (Peanut ALlergy oral Immunotherapy Study
of AR101 for DEsensitization in children and adults) was
an international, randomized 3:1, double-blind, placebo-controlled,
Phase 3 trial of the efficacy and safety of AR101 in a Characterized
Oral Desensitization ImmunoTherapy (CODIT™)
approach in patients with peanut allergy. PALISADE enrolled 554
peanut-allergic patients ages 4–49 (499 ages 4–17) at more than 60
clinical sites in the United States, Canada, and eight countries in the
European Union. To meet PALISADE’s inclusion criteria, patients had to
experience dose-limiting symptoms at or before the 100-mg dose of peanut
protein in an entry DBPCFC, which allowed consecutive doses of 1, 3, 10,
30 and 100 mg of peanut protein, given 20 to 30 minutes apart. Patients
enrolled in PALISADE underwent a dose escalation period of approximately
22 weeks to reach a maintenance dose of 300 mg per day of AR101 or
placebo, then continued with daily maintenance at 300 mg per day of
AR101 or placebo for approximately six months. At the end of the
maintenance period, patients underwent an exit DBPCFC, which tested
consecutive doses of 3, 10, 30, 100, 300, 600 and 1000 mg of peanut
protein, given 20 to 30 minutes apart, as tolerated with no or only mild
symptoms. Following the completion of the challenge, patients were
unblinded and eligible to rollover or crossover into the follow-on
ARC004 clinical trial, as appropriate.

Aimmune plans to present data from the PALISADE trial in a late-breaking
oral abstract presentation at the 2018 American Academy of Allergy,
Asthma & Immunology–World Allergy Organization Joint Congress in
Orlando. Dr. Stacie Jones of the University of Arkansas will present
“Efficacy and Safety of AR101 in Peanut Allergy: Results from a Phase 3,
Randomized, Double-Blind, Placebo-Controlled Trial (PALISADE)” in
Session 3609 on Sunday, March 4, from 2:00 to 3:15 p.m. EST.

About Aimmune’s Phase 3 Program for AR101

Aimmune has three active Phase 3 AR101 studies underway. The open-label
follow-on trial to PALISADE, ARC004, crossed PALISADE placebo patients
over to active treatment and rolled AR101 patients over to extended
maintenance, with different dose frequency intervals; Aimmune plans a
data cut from this trial in the third quarter of 2018. Aimmune expects
data from the RAMSES trial, taking place in the United States and Canada
and designed to illuminate real-world patient and allergist experiences
with AR101, in the second half of 2018, followed by data from the
ARTEMIS trial, a dedicated European study of AR101, in early 2019.

About AR101

AR101 is a novel, investigational oral biologic drug for use in oral
immunotherapy (OIT) in patients with peanut allergy. The drug, which is
manufactured in accordance with current Good Manufacturing Practices
(cGMP), has a characterized protein profile found in peanuts, analyzed
to ensure consistent major allergen content. The amount of active
ingredient in each AR101 capsule is controlled to ensure minimal
variability of allergen content across doses of a given strength.

About Aimmune Therapeutics

Aimmune Therapeutics, Inc., is a clinical-stage biopharmaceutical
company developing treatments for potentially life-threatening food
allergies. The company’s Characterized Oral Desensitization
ImmunoTherapy (CODIT™) approach is intended to achieve meaningful levels
of protection by desensitizing patients with defined, precise amounts of
key allergens. Aimmune’s first investigational biologic product using
CODIT™, AR101 for the treatment of peanut allergy, has received the
FDA’s Breakthrough Therapy Designation for the desensitization of
peanut-allergic patients 4–17 years of age and is currently being
evaluated in Phase 3 clinical trials. For more information, please see www.aimmune.com.

Forward-Looking Statements

Statements contained in this press release regarding matters that are
not historical facts are “forward-looking statements” within the meaning
of the Private Securities Litigation Reform Act of 1995. Because such
statements are subject to risks and uncertainties, actual results may
differ materially from those expressed or implied by such
forward-looking statements. Such statements include, but are not limited
to, statements regarding: Aimmune’s expectations regarding the potential
benefits of AR101; Aimmune’s expectations regarding potential
applications of the CODIT™ approach to treating life-threatening food
allergies; Aimmune’s expectations regarding the availability of
additional AR101 data in March 2018 at AAAAI-WAO; Aimmune’s expectations
regarding its clinical trials of AR101, including the timing of the
completion of such trials and the availability of data from such trials;
Aimmune’s ability to develop and advance additional product candidates
into and successfully complete clinical trials; and Aimmune’s
expectations regarding the timing of potential regulatory filings for
AR101. Risks and uncertainties that contribute to the uncertain nature
of the forward-looking statements include: the expectation that Aimmune
will need additional funds to finance its operations; the company’s
ability to initiate and/or complete clinical trials; the
unpredictability of the regulatory process; the possibility that the
results of early clinical trials may not be predictive of future
results; the possibility that Aimmune’s clinical trials will not be
successful; Aimmune’s dependence on the success of AR101; the company’s
reliance on third parties for the manufacture of the company’s product
candidates; possible regulatory developments in the United States and
foreign countries; and Aimmune’s ability to attract and retain senior
management personnel. These and other risks and uncertainties are
described more fully in Aimmune’s most recent filings with the
Securities and Exchange Commission, including its Quarterly Report on
Form 10-Q for the quarter ended September 30, 2017. All forward-looking
statements contained in this press release speak only as of the date on
which they were made. Aimmune undertakes no obligation to update such
statements to reflect events that occur or circumstances that exist
after the date on which they were made.

This press release concerns a product that is under clinical
investigation and that has not yet been approved for marketing by the
U.S. Food and Drug Administration (FDA) or the European Medicines Agency
(EMA). It is currently limited to investigational use, and no
representation is made as to its safety or effectiveness for the
purposes for which it is being investigated.